Personally I would not tell her I was digging so deep into her family members' social media. She might feel threatened and react badly. If I were you I would maybe bring it up in general at one point that you feel you have a problematic way of googling and then feeling bad. I would just try not to carry on doing it and finding new info and forget about this instance and not bring it up, as it is highly personal. Maybe you could block her yourself to avoid the temptation to search again?